Throw DOS api away, re-layout memory to fit CP/M model
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2935d7ee6c
commit
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60
boot/fat.asm
60
boot/fat.asm
@ -1,13 +1,15 @@
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; Memory layout:
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%define self 0x00600 ; 1 sector
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%define fattab 0x01000 ; variable size
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%define rootdir 0x06000 ; variable size
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%define config 0x07800
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%define prog 0x07C00
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%define segment 0x00100
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%define self (0x7C00-(segment<<4)) ; 1 sector
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%define fattab (self+0x200) ; variable size
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%define rootdir 0x00100 ; variable size
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%define prog 0x0F000 ; 4K at the end for OS
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org self
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jmp short init
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dw self
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cluster_offset:
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dw 0
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@ -58,23 +60,16 @@ times (62 - ($-$$)) nop
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init:
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cli
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; Stack grows down from 64k
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xor ax, ax
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mov ss, ax
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mov sp, ax
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; Relocate from [prog] to [self]
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mov ds, ax
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mov es, ax
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mov si, prog
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mov di, self
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mov cx, 0x100
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rep movsw
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jmp 0:main
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jmp segment:main
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main:
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; Stack grows down from 64k
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mov ax, cs
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mov ss, ax
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mov sp, prog
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mov ds, ax
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mov es, ax
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mov [fdc.drv], dl ; save drive number in fd
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sti
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@ -110,31 +105,10 @@ main:
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mov bp, 0x3332
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jc error
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; Load config file after kernel
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push bx
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mov ax, config_name
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call load_file
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pop bx
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; Write a null byte after config file
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mov BYTE [bx+di], 0
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; Setup registers for kernel
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xor ax, ax
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; CX is size of config
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mov cx, di
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; DL is drive number
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xor dx, dx
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mov dl, [fdc.drv]
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; BX is offset of config
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sub bx, prog
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; the pointers are 0
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xor bp, bp
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xor si, si
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xor di, di
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; jump into kernel
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jmp (prog>>4):0
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jmp segment:prog
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; Load a file into memory
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; IN AX pointer to 8.3 filename
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@ -260,8 +234,6 @@ error:
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int 0x16
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int 0x19
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config_name:
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db "RCONFIG SYS"
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kernel_name:
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db "RDOS SYS"
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@ -1,35 +0,0 @@
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; Reads a single character with echo
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; out AL character
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isr_getc_echo:
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xor ax, ax
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int 0x16
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test al, al
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jz isr_getc_echo
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call putc
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iret
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; Reads a single character without echo
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; out AL character
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isr_getc:
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xor ax, ax
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int 0x16
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test al, al
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jz isr_getc
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iret
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; Prints a single character
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; in DL character
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isr_putc:
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push ax
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mov al, dl
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call putc
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pop ax
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iret
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putc:
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push bx
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mov ah, 0x0e
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mov bx, 0x0000
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int 0x10
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pop bx
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ret
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@ -1,53 +0,0 @@
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; drive table
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%define drivetab_type 0x00 ; BYTE 0=unassigned, 1=BIOS/CHS, 2=BIOS/LBA
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%define drivetab_num 0x01 ; BYTE DL number
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; CHS data for type=1
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; Might be reused for driver address
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%define drivetab_heads 0x02 ; WORD CHS heads
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%define drivetab_spt 0x04 ; WORD CHS sectors per track
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%define drivetab_sectors 0x06 ; DWORD total number of sectors
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%define drivetab_offset 0x0A ; DWORD partition offset
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%define drivetab_size 0x0E
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drive_table:
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dw 0
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.count:
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dw 4
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; DI is incremented for the space taken
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; IN ES:DI
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drive_setup:
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xor cx, cx
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mov [drive_table], di
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mov al, drivetab_size
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mov ah, BYTE [drive_table.count]
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mul ah
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xchg cx, ax
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; this increments DI and also fills table with zeros
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rep stosb
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ret
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; Load a drive table entry
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; IN DL drive number
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; OUT DS:SI ptr to table item
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drive_load:
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; bail out if number too high
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cmp dl, [cs:drive_table.count]
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jnc .err
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push cs
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pop ds
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mov si, [drive_table]
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push ax
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mov al, drivetab_size
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mul dl
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add si, ax
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pop ax
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ret
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.err:
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stc
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ret
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@ -1,30 +0,0 @@
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; Register a interrupt handler (21h AH=25h)
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; in: AL interrupt number
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; DS:DX far ptr
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isr_intr_register:
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; backup previous stos ptr
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push es
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push di
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; DI = AL * 4
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mov ah, 4
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mul ah
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mov di, ax
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; ES = 0
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xor ax, ax
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mov es, ax
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; store offset
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mov ax, dx
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stosw
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; store segment
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mov ax, ds
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stosw
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; restore previous stos ptr
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pop di
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pop es
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iret
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@ -1,64 +1,57 @@
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cpu 8086
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org 0x0
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; Memory layout (starting from top)
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%define self 0xF000
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%define diskbuf (self-0x200)
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%define stack (diskbuf) ; end addr, grows down
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org self
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jmp init
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isr_dos_main:
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cmp ah, 0x01
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je isr_getc_echo
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cmp ah, 0x02
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je isr_putc
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cmp ah, 0x25
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je isr_intr_register
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jmp isr_invalid
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banner:
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db "RDOS 2019-09", 0x0A, 0x0D, 0
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%include "intr.asm"
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%include "chario.asm"
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; ISR for invalid subfunctions or unimplemented
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isr_invalid:
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mov bp, 0xFEFE
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int3
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.hlt:
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hlt
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jmp .hlt
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; ISR tail to set carry flag to signal error
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isr_error:
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push bp
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mov bp, sp
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; set carry flag
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or WORD [SS:BP+6], 1
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pop bp
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isr_return:
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iret
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%include "drive.asm"
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print_banner:
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mov cl, 2
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mov si, banner
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.loop:
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mov dl, BYTE [si]
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test dl, dl
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jz .end
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call cpm_syscall
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inc si
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jmp .loop
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.end:
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ret
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init:
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mov ax, cs
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mov ds, ax
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mov es, ax
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mov sp, stack
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call config_first_run
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mov di, kernel_end
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call drive_setup
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mov dx, isr_dos_main
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mov ax, 0x2521
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pushf
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push cs
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call isr_dos_main
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mov dl, 0x37
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mov ah, 0x02
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int 0x21
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call print_banner
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int3
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cli
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.halt:
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hlt
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jmp .halt
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cpm_syscall:
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cmp cl, 0x02
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je putc
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stc
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ret
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putc:
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push ax
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push bx
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mov al, dl
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mov ah, 0x0e
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mov bx, 0x0000
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int 0x10
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pop bx
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pop ax
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ret
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%include "string.asm"
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%include "config.asm"
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kernel_end:
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